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Physics · 2025 · 3 marks
Dual Nature of Radiation and MatterPhotoelectric Effect and Wave Theory of Light3 marksApplyshort answer
CBSE 2025 · Region 1 · Set 3 · Q26
(a) Mention any three features of results of experiment on photoelectric effect which cannot be explained using the wave theory of light. (b) In his…
(a)
Mention any three features of results of experiment on photoelectric effect which cannot be explained using the wave theory of light.
(b)
In his experiment on photoelectric effect, Robert A. Millikan found the slope of the cut-off voltage versus frequency of incident light plot to be $\displaystyle 4.12 \times 10^{-15}$ Vs. Calculate the value of Planck's constant from it.
Marking-scheme solution
(a)
Three features:
(i)
The existence of threshold frequency $\displaystyle \left(\nu_{0}\right)$.
(ii)
Maximum kinetic energy of photoelectrons is independent of intensity of incident radiation.
(iii)
Instantaneous nature of photoelectric effect.
(b)
slope $\displaystyle =\frac{h}{e}$
$\displaystyle \therefore h=e \times$ slope
$\displaystyle =1.6 \times 10^{-19} \times 4.12 \times 10^{-15}$
$\displaystyle =6.6 \times 10^{-34} \mathrm{~Js}$
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